Dark trace cathode ray tube erase system

ABSTRACT

A flash erasure system for erasing the display on a dark trace cathode ray tube. The system includes a number of flash tubes which can be selected for operation in a predetermined sequence. This mode of operation allows a cooling and charging period for each tube before it is required to be used again.

United States Patent A 1111 3,777,213

Hankins et al. 1 Dec. 4, 1973 DARK TRACE CATHODE RAY TUBE ERASE SYSTEM[56] References Cited [75] Inventors: Harold Charles Arthur Hankins,UNITED STATES PATENTS Glosson; lmad Shakir Torsun, 3,488,558 1 1970Grafton 315 313 x Manchester, both of England 3,142,780 7/1964 Rich 315323 x 3,484,626 12/1969 Grafham 315 323 x [73] Assignee: InternationalComputers Limited,

Putney London England Primary Examiner-Alfred L. Brody [22] Filed: Nov.12, 1971 Attorney-Frederick E. l-Iane et al.

[21] Appl. No.: 198,224

. I [57] ABSTRACT A flash erasure system for erasing the display on a 30F I: t Pri D ta 1 V orelgn App ca onty a dark trace cathode ray tube.The system includes a Feb. 20, 1970 Great Bl'ltall'l 55,175/70 number oftubes wich can be Selected for p tion in a predetermined sequence. Thismode of oper 5" 315/ 15; ation allows a cooling and charging period foreach t d t [58] Field of Search 315/313, 315, 323, befme requ're be usedagam 315/241 R, 241 P, 241 s 1 Claim, 1 Drawing Figure FLASH TUBECONTROL} i Z 5 4 FLASH TUBEJ CONTROLS 20 T T T 14 1'5 16 CONTROL 1 UNIT\22 1 7 RECIRCULATING 23 STEPPING 24 COUNTER BACKGROUND OF THE INVENTIONThe present invention relates to information processing apparatusutilizing dark trace cathode ray tubes for information storage ordisplay for computers, and in particular to erasing devices for suchtubes.

It has previously been proposed to erase the image displayed on the faceof a dark trace cathode ray tube by exposing the face to heat obtainedfrom, for, example, a photoflood lamp. A tendency has also previouslybeen noted that such erasure is obtainable from a single flash tube.However, where erasure is required at a high cyclic frequency such asingle flash tube is not suitable as an erasure device since it requiresa fairly lengthy period between flashes in order for the tube to becomecool and for an associated driving capacitor to be recharged.

SUMMARY OF THE INVENTION According to the present invention informationprocessing apparatus utilizing a dark trace cathode ray tub and a traceerasing device includes a plurality of flash tubes; circuit meansassociated with each flash tube including a capacitor connected acrossthe tube; means for charging the capacitors at a predetermined rate; anderasing control means operable to apply a triggering signal to each tubein a predetermined sequence, each tube being responsive to thetriggering signal to produce a flash.

BRIEF DESCRIPTION OF THE DRAWING Apparatus embodying the presentinvention will now be described, by way of example, with reference tothe accompanying drawing which shows in schematic form a trace erasingdevice.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawing,four flash tubes 1, 2, 3, 4 are connected respectively to flash tubecontrol circuits 5, 6, 7, 8. The control circuits each include acapacitor and a resistor and are similar to conventional circuits thatare used to operate electronic flash guns in the photographic field. Thetrigger electrodes 9, 10, l 1, 12 of the four flash tubes are connectedone to each of the four stages 13, l4, l5, 16 of a recirculatingstepping counter 17 through four capacitors 18, 19, 20, 21. Each of thestages of the stepping counter is bistable and the arrangement is suchthat one stage is in a first state and the other three stages are in theopposed state. Stepping signals are applied to the counter on line 22and a recirculating line 23 enables the state of stage 16 to be steppedon to stage 13. The stepping signals are derived from a control unit 24,and will be referred to hereafter as erase signals. It will beunderstood that the flash tube control circuits 5, 6, 7, 8, therecirculating stepping counter 17 and the control unit 24 share a commonpower source (not shown) and therefore have a common earth connection.

In operation, when the device is switched on the rev circulatingstepping counter is forcibly reset so that, for example, stage 13 is setto the first state and the other three stages are set to the opposedstate. An erase signal from the control unit 24 over line 22 to thecounter 17 is efiective to causethe first state to be stepped from stage13 to stage 14.. As stage 14 of the counter switches to the first statea stepped waveform is applied to capacitor 19 which produces a pulse onthe appropriate trigger line effective to cause the flash tube 2 toproduce a single flash in the conventional manner.

Each subsequent erase signal steps on the first state by I one stage inthe counter with the result that the flash tubes 3,4, l, 2 are triggeredin turn in cyclic order. It will be realised that after each operationof any one of the flash tubes the driving capacitor which is containedin the associated flash tube control circuit is recharged in theconventional manner in readiness for the next occurring triggeringsignal at the appropriate trigger electrode.

By using a number of flash tubes in the way described it is possible toensure that unwanted'heat is dissipated from each tube before it isrequired for re-use after it has once been used. The number of flashtubes provided is chosen in dependence upon the frequency of erasurerequired. Provision of a number of flash tubes also enables aconservative charging current to be used for the flash tube drivingcapacitors. It has been found that using the arrangement of four flashtubes as described enables a display tube to be used to displayinformation which is regenerated at a frequency of some five to eightcycles a second, for example, which is sufficient to produce a visuallystable display, and in which the information has been modified oneach'successive display cycle. The provision of the required number offlash tubes together with the triggering signal cyclic distributiondescribed enables the displayed information to be erased at the end ofeach display cycle, so that the displayed information may be constantlychanging, and this continual modification is then possible withoutsignificant reduction in the repetition rate of the display cycles Weclaim:

1. A dark trace cathode ray tube erase system, comprising a plurality offlash tubes each having a triggering electrode and disposable to erase adark trace cathode ray tube; a recirculating stepping counter having acounter stage for each said tube; the output of each stage beingconnected to a triggering electrode of the associated tube and arrangedsuch that when any stage of the counter is in a first state in which itis able to apply a triggering pulse to its associate tube to cause thelatter to produce a flash, the remaining stages are forced into theopposed state; and a control unit for applying stepping pulses to thecounter to cause the latter to apply a triggering signal to each tube ina predetermined sequence.

1. A dark trace cathode ray tube erase system, comprising a plurality offlash tubes each having a triggering electrode and disposable to erase adark trace cathode ray tube; a recirculating stepping counter having acounter stage for each said tube; the output of each stage beingconnected to a triggering electrode of the associated tube and arrangedsuch that when any stage of the counter is in a first state in which itis able to apply a triggering pulse to its associate tube to cause thelatter to produce a flash, the remaining stages are forced into theopposed state; and a control unit for applying stepping pulses to thecounter to cause the latter to apply a triggering signal to each tube ina predetermined sequence.